# mbus-core
`mbus-core` is a helper crate for [modbus-rs](https://crates.io/crates/modbus-rs).
It provides shared protocol types, transport abstractions, function-code definitions,
and data models used by higher-level crates such as `mbus-client`, `mbus-tcp`, and
`mbus-serial`.
## What This Crate Provides
- Core Modbus ADU/PDU data structures.
- Function code enums and protocol constants.
- Transport trait and transport configuration types.
- Shared error model (`MbusError`) used across the workspace.
- Feature-gated Modbus data models (coils, registers, etc.).
- `no_std`-friendly implementation for embedded targets.
## Helper Crate Role in the Workspace
`mbus-core` is intentionally low-level and reusable.
- `mbus-client` builds request/response workflows on top of this crate.
- `mbus-tcp` and `mbus-serial` implement concrete transport layers that satisfy
interfaces defined here.
- `modbus-rs` re-exports major crates for easier consumption.
This separation keeps protocol definitions centralized and avoids duplication across
client and transport crates.
## Module Overview
- `data_unit`: ADU/PDU structures and framing helpers.
- `errors`: Core error types used by all crates.
- `function_codes`: Public and user-defined function code definitions.
- `models`: Feature-gated Modbus data models.
- `transport`: Transport traits, config types, and transport-related enums/errors.
## Feature Flags
`mbus-core` supports selective compilation to reduce binary size.
Available feature flags:
- `serial-ascii`
- `coils`
- `registers`
- `discrete-inputs`
- `fifo`
- `file-record`
- `diagnostics`
Default behavior:
- `default` enables all features above.
`serial-ascii` affects ADU buffer sizing:
- enabled: `MAX_ADU_FRAME_LEN = 513` (ASCII upper bound)
- disabled: `MAX_ADU_FRAME_LEN = 260` (TCP/RTU upper bound)
This reduces stack usage in non-ASCII builds while preserving full ASCII compatibility
when explicitly enabled.
Example with selective features:
```toml
[dependencies]
mbus-core = { version = "0.2.0", default-features = false, features = ["coils", "registers"] }
```
## no_std
This crate is designed for embedded and constrained environments and is compatible
with `no_std` usage patterns.
## License
Copyright (C) 2025 Raghava Challari
This project is currently licensed under GNU GPL v3.0.
See [LICENSE](./LICENSE) for details.
## Disclaimer
This is an independent Rust implementation of the Modbus specification and is not
affiliated with the Modbus Organization.
## Contact
For questions or support:
- Name: Raghava Ch
- Email: [ch.raghava44@gmail.com](mailto:ch.raghava44@gmail.com)